There is much debbate on this in the industry. Studies have shown that boosting the N(itrogen) increases the leaf area of a plant without increasing photosynthesys in the leaves. There is some logic to this since a straight NPK fert is not adding any of the other elements that are constituant to the chloroplasts. There are other studise that show small plants like crabapple are more suseptable to pests with boosted N.
Most of the studies done previously are based of agronomic science of annual crops (soy, wheat, corm...)
I am in the camp that see this logic. If we are going to boost these three values then we shoul be boosting the minor and trace elements. I've used both fish and seaweed emultions for this in the past.
http://search.dogpile.com/texis/search?q=proper+pruning&geo=no&fs=web
On old trees i usualy recomend deadwood removal only.
Another option is to mulch the area as far out as possible with a composted organic, then manybe top dress with an ornimental mulch. (bark..) For oaks I usualy recomend using a pine compost since it is acidic and will be less likely to pass diseases on. A composted manure base would be good to.
The need for compost is because the initial brakdown will use a lot of N from th soil. This can "rob" the tree and be counter productive.
Also do not pile the mulch on the trunk, and have it only 3 inches deep. Contact can cerate moist conditions that can cause root/basal rot.
How wide of a mulch ring? As wide as you can aestheticly stand it then one foot more
.
lastly there is a new tool in our industry called an Air Spade. It is a pnumatic too that can blast the soil away and not damage the roots. A contractor with this could amned the soil so that there is a better environment for the trees roots.
Here is som reading so that you can be a better informed consumer when choosing a tree service.
